The purpose of this study was to investigate the effectiveness of the conceptual change text oriented instruction over traditionally designed instruction on ninth grade students' understanding of the human circulatory system concepts, and their retention of this understanding. The subjects of this study consist of 73 ninth grade female students from two classes of a basic school in Jordan. One of the classes was randomly assigned as an experimental group in which conceptual change text oriented instruction was implemented, and the other class was randomly assigned as a control group in which students were instructed by traditionally designed biology instruction. Results showed that students exposed to conceptual change oriented instruction had better understanding of the human circulatory system concepts than those exposed to traditional instruction. The results also showed that the conceptual change text oriented instruction was significantly better than the traditional instruction in retention of this understanding. (Contains 2 tables.) [Appended to this document are: "Appendix A. Human Circulatory System Concepts Test" and "Appendix B. Students' Misconceptions Concerning the Human Circulatory System."]